INTERNAL EROSION OF VOLCANIC COARSE GRAINED SOILS AND ITS EVALUATION

Abstract

This paper aims at revealing mechanical behavior of volcanic coarse grained soils subjected to
seepage flow. In order to accomplish the purposes, a series of upward seepage tests was conducted to grasp piping
phenomenon in compacted volcanic soils and to investigate the effects of differences in compaction conditions on
its behavior. In the experiments, the movement of soil particles in seepage flow tests was observed using an X-ray
CT scanner in detail. The test results showed that destabilization of soil structures due to seepage flow is changed
depending on an increase of amount of finer soil particles, and that internal erosion is induced by loss of fine
particles with the changes in void ratio. As a result, a significant variation in hydraulic conductivity was generated.
Additionally, internal stability of volcanic soils under several geotechnical conditions was elucidated by empirical
criterion. In the consideration of the results, it was shown that volcanic coarse grained soil including pumice
particles with a low specific gravity was internally unstable. Based on the results, a geotechnical evaluation was
discussed for the stability of soil structures such as embankments constructed by volcanic coarse grained soils.